At the time, using the word that directly translates to "black" in English "preto", was considered extremely offensive and was never to be used applied to a person.
Now, fast-forward a few years and the influence of American woke culture, the word "negro" is now connected with the N-word slur in English and is considered offensive. You now have people of colour demanding to be called "preto".
This is one of the many insanities that the woke movement brought us. I'm glad the world is changing away from it.